Antimetabolites such as 5-fluorouracil and 5-azacytidine are believed to exert antitumor effects through their incorporation into mRNA, and hence interference with the ability of mRNA to code for proteins critical to the balanced growth of the cell. This hypothesis will be tested by quantitative and qualitative assessment of the capacity of L1210 poly(A) mRNA from drug-treated tumor-bearing mice to code for proteins in an in vitro heterologous translation system. These studies will include an analysis of both the 5' cap and 3'-poly(A) structures of mRNA, as well as the synthesis of the mRNA in vivo. This experimental system will allow an assessment of the effect of anticancer drugs on the synthesis, post-transcriptional processing and coding properties of tumor mRNA.